A class of polymers known as polyimides has become known for its combination of good heat stability and high upper use temperatures, as measured by glass transition temperature. A particularly useful type of such polyimides is known as polyimidesiloxanes.
Because of their combination of properties, polyimidesiloxanes have been used in electronic applications, particularly in microelectronic components in the integrated circuit industry.
Because many of the previously known polyimidesiloxanes are insoluble or difficultly soluble in solvents, when used in the microelectronics industry, there is a great need for polyimidesiloxanes having improved solubility characteristics, as well as a better balance of heat resistance and upper use temperature.
The chemistry for making polyimides has been well-known since about 1960. A structurally simple polyimide can be prepared by reacting a diamine with a dianhydride. ##STR6##
The first step, or the polycondensation reaction, generates polyamide acids which are hydrolytically unstable even at room temperature. The second step, or the imidization reaction, produces the stable polyimides desired for various applications.
Polyimidesiloxanes can be prepared by reactions employing siloxane diamines or siloxane dianhydrides with organic comonomers. Polyimidesiloxanes can also be prepared from siloxane diamines and siloxane dianhydrides without an organic comonomer.
The first polyimidesiloxane was prepared by reacting pyromellitic dianhydride (PMDA) with 1,3-bis-(aminopropyl)-1,1,3,3-tetramethyl disiloxane in 1966 (see V. H. Kuckertz, Macromol. Chem. 98, 1966, pp. 101-108). This polyimidesiloxane is a crystalline material and cannot be cast into flexible films from solvent. Polyimidesiloxanes derived from reactions of benzophenone tetracarboxylic dianhydride (BTDA) and .alpha.,w-diamino organo-polysiloxanes were disclosed by General Electric in 1967 in U.S. Pat. No. 3,325,450. Polyimidesiloxanes containing an .alpha.,w-diamino organo-polysiloxane and a diether dianhydride (DEDA) have also been disclosed in U.S. Pat. No. 3,847,867.
All these BTDA and DEDA containing polyimidesiloxanes are amorphous materials. They have a glass transition temperature of no more than 100.degree. C. and, therefore, have very limited upper use temperatures, despite the excellent thermal stability of these polymers up to about 200.degree. C.
Polyimidesiloxanes containing both organic and siloxane monomers have been reported for PMDA containing copolymers (see Japan Kokai Tokkyo Koho 83/7473 and 83/13631); for BTDA containing copolymers (U.S. Pat. Nos. 3,553,282 and 4,404,350) and for diether dianhydride containing copolymers (U.S. Pat. No. 3,847,867). These PMDA containing polyimidesiloxanes are not soluble in any solvent. The BTDA containing polyimidesiloxanes are only soluble in high boiling or toxic solvents such as 1-methyl-2-pyrrolidinone, commonly known as N-methyl pyrrolidone (NMP), phenol or cresol, and the like. The diether dianhydride containing polyimidesiloxane, in addition, are also soluble in chlorinated solvents such as dichlorobenzene and dichloromethane. Since these phenol and chlorinated compounds are both corrosive and highly toxic, the polyimidesiloxanes have limited application in coating applications, especially in heat sensitive electronic devices. This is also due to the fact that a NMP soluble polyimidesiloxane normally has to be heated to 350.degree. C. for at least half an hour to remove all the residual solvent in a film having a micron-thickness film.
Only a few polyimidesiloxanes are soluble, even in high boiling and relatively toxic solvents, such as 1-methyl-2-pyrrolidinone (NMP), despite the fact that most of their polyamide acids are soluble. The usage of polyamide acids in coating applications has many drawbacks. First, a subsequent imidization reaction on substrates produces water. Therefore, it can only be used in very thin film coatings and where void-free property is not critical to performance. Second, the removal of high boiling, polar solvents, such as NMP, requires temperatures as high as 350.degree. C. for about 30 minutes even for films of a micron thickness. This drying process is not only energy intensive, but also unacceptable to some heat sensitive electronic devices or substrates. In addition, the polyamide acids solution has to be stored at refrigeration temperature (&lt;4.degree. C.) and it still has a very short shelf life (about 3 months). Finally, only the fully imidized polyimidesiloxanes are thermally stable for melt processing such as extrusion and injection molding. A soluble polyimidesiloxane can be fully imidized at temperatures of about 160.degree. to 170.degree. C. in a solvent, whereas imidization for insoluble polyimidesiloxanes in the solid state may require temperatures 50.degree. C. above their glass transition temperatures which can be as high as 200 to 250.degree. C. Shaping not fully imidized polyimidesiloxanes by the melt processing method produces voids in the products and often is not desirable.
A variety of organic dianhydrides have been used in making soluble polysiloxaneimides. Some of these dianhydrides are disclosed in my copending applications as follows.
My copending application Ser. No. 239,372, filed Sept. 1, 1988, as a continuation-in-part of Ser. No. 032,722, filed Mar. 31, 1987, discloses that fully imidized polyimidesiloxanes made from oxydiphthalic anhydrides are soluble in solvents such as diglyme, tetrahydrofuran and methyl ethyl ketone.
My copending application Ser. No. 154,168 filed Feb. 9, 1988, discloses that substantially fully imidized polyimidesiloxanes made from a mixture of a biphenyl tetracarboxylic dianhydride and a benzophenone tetracarboxylic dianhydride are soluble in solvents such as diglyme, tetrahydrofuran and methyl ethyl ketone.
My copending application Ser. No. 153,898, filed Feb. 9, 1988, discloses that substantially fully imidized polyimidesiloxanes made from a bis(dicarboxyphenyl)hexafluoropropene dianhydride and mixtures with other dianhydrides are soluble in solvents such as diglyme, tetrahydrofuran and methyl ethyl ketone.
My copending application Ser. No. 205,412, filed June 10, 1988, discloses that substantially fully imidized polyimidesiloxanes made from sulfurdiphthalic anhydride are soluble in solvents such as diglyme, tetrahydrofuran and methyl ethyl ketone.
U.S. Pat. No. 4,535,099 describes a polyimide prepared from the reaction of an organic tetracarboxylic acid or derivative thereof with a mixture of an aromatic diamine and an amine-terminated silicone. Disclosed as suitable diamines are diamine pyridines, which are diprimary monotertiary amines. The polyimides are particularly useful in the preparation of flexible foams.
The above-noted U.S. Pat. No. 3,553,282 discloses making polyamic acids that may include 2,6-diaminopyridine. The patent does not teach how to make fully imidized and soluble polyimidesiloxanes. More specifically, the patent does not teach how to make a fully imidized, yet soluble, polyimidesiloxane from 2,6-diaminopyridine and dianhydrides such as BTDA and 6FDA.
A purpose of the present invention is to make novel polyimidesiloxanes.
Another purpose of the present invention is to develop a fully imidized polyimidesiloxane which is soluble in low boiling, non-polar and non-toxic solvent such as diglyme. Another purpose of the present invention is to develop the desirable polyimidesiloxanes based on less expensive and readily available organic monomers. Another purpose of the present invention is to develop less expensive polyimidesiloxane which can be readily scaled-up into commercially available, large scale production. Another purpose of the present invention is to develop less expensive polyimidesiloxanes which can be used in price sensitive applications or in favorable competitive performance/cost positions in cable jacket, as well as 3D molded wire board applications and where high volume and low price are essential.
Another purpose of the invention is to provide fully imidized polyimidesiloxanes which are soluble not only in high boiling solvents, such as NMP, but also in low boiling, low toxic, less polar solvents such as diglyme or tetrahydrofuran (THF). A further purpose of the invention is to provide polyimidesiloxanes that have a good balance of heat resistance and high upper use temperatures, as measured by glass transition temperatures.
Another purpose of this invention is to produce curable and cross-linked polyimidesiloxanes.